1. Field of the Invention
The present invention relates to a structure supporting apparatus and, more specifically, to a structure supporting apparatus interposed between an upper structure and a lower structure of a structure, such as a bridge and an express-highway, comprising the upper structure and the lower structure for supporting the upper structure.
2. Description of Background Art
A structure composed of an upper structure 1 and a lower structure 2 for supporting the upper structure 1, such as, for example, a bridge and an express-highway, includes supporting members 3 which are interposed between the upper structure 1 and the lower structure 2, as shown in FIG. 1, to surely transmit vertical load of the upper structure 1 to the lower structure 2 or absorb expansion of the upper structure 1 resulting from temperature change or horizontal swinging motion of the same.
The supporting members 3 become fatigued for many years of use and thus must be replaced with new ones after a set period of time. For this, there has been proposed a supporting apparatus disclosed by, for example, Japanese Laid-open Patent Publication No. Hei 7(1995)-166514 and shown in FIGS. 10 to 12.
As shown in FIG. 10, the supporting apparatus comprises an upper pressure-bearing member 5 having at its bottom surface a lower sliding surface 4 of a slant surface, a lower pressure-bearing member 7 laid over the upper pressure-bearing member 5 and having at its top surface an upper sliding surface 6 of a slant surface which is slidable over the lower sliding surface 4 of the upper pressure-bearing member 5, and a hydraulic jack 8 for pulling the lower pressure-bearing member 7 to move it. In use, the supporting apparatus is first interposed between the upper structure 1 and the lower structure 2 in the state of the upper pressure-bearing member 5 and the lower pressure-bearing member 7 being displaced with each other in an axial direction. At that time, a tread 11 is interposed between the upper structure 1 and the upper pressure-bearing member 5 and also a base member 12 is interposed between the lower structure 2 and the lower pressure-bearing member 7. The upper pressure-bearing member 5, which has a projection 9 projecting from a bottom surface thereof, is laid so that the projection 9 can be inserted in a groove 10 formed in the upper pressure-bearing member 5. Further, a reaction bearing member 13 is interposed between the upper pressure-bearing member 5 and the hydraulic jack 8.
Subsequently, the hydraulic jack 8 is driven to pull the lower pressure-bearing member 7 toward the hydraulic jack 8, as shown in FIG. 11. The upper pressure-bearing member 5 is then pushed by the as-pulled lower pressure-bearing member 7, but is not moved, because the upper pressure-bearing member 5 is received by the reaction bearing member 13. Only the lower pressure-bearing member 7 is moved while the upper sliding surface 6 and the lower sliding surface 4 are in sliding engagement with each other. As a result of this, the thickness of the upper pressure-bearing member 5 and lower pressure-bearing member 7 in their overlaying direction becomes gradually increased. As a result of this, the supporting apparatus lifts up the upper structure 1 with respect to the lower structure 2, while supporting the upper structure 1 thereon.
Then, after the upper structure 1 is raised up to a suitable position with respect to the lower structure 2, stop members 14 are fitted into a space in the groove 10 in which the projection 9 is received, as shown in FIG. 12, to restrict relative movement between the upper pressure-bearing member 5 and the lower pressure-bearing member 7, so as to keep the upper structure 1 in the suitable position with respect to the lower structure 2.
This type of supporting apparatus enables the upper structure 1 to be lifted up in the state of being supported against the lower structure 2 and also can be used as the supporting member 3 as it is, thus having the advantage of permitting easy replacement of the supporting member 3, even in a case where there is no working room for removing the existing supporting member 3.
With this type of supporting apparatus, the upper structure 1 must be lifted up to a precise position with respect to the lower structure 2 and, accordingly, the lower pressure-bearing member 7 must be moved with accuracy. However, with the supporting apparatus disclosed by the JP Laid-Open Patent Publication No. Hei 7(1995)-166514 using the hydraulic jack 8 to move the lower pressure-bearing member 7, in the event that for example a hose of the hydraulic jack 8 is damaged and hydraulic pressure is decreased, there can be produced the disadvantages that the lower pressure-bearing member 7 can not be moved precisely and that the upper structure 1 as lifted is lowered. Further, since the hydraulic pressure in the hydraulic jack 8 decreases over a period of time, it is necessary that after the upper structure 1 is raised up to a suitable position with respect to the lower structure 2, the stop members 14 are fitted into the space in the groove 10 to restrict the relative movement between the upper pressure-bearing member 5 and the lower pressure-bearing member 7. Thus, the known supporting apparatus has the disadvantages of taking many processes and troublesome works.
On the other hand, for example when a gear transmission mechanism or equivalent is used instead of the hydraulic jack 8, the above-mentioned disadvantages caused by the decrease in hydraulic pressure may be avoided. But, since the gear transmission mechanism is, in general, not so high in the efficiency and also may cause the output power to vary with respect to the input power, it is hard to move the lower pressure-bearing member 7 with accuracy.